This invention relates to a heat pipe stabilised specimen container and is particularly concerned with a container suitable for location within the core of a liquid metal cooled fast breeder reactor so that certain properties, such as creep strength and ductility, of specimens can be investigated under high temperature conditions and when subject to irradiation. A specific application of the invention is in the investigation of fuel pin cladding materials.
The high temperature sensitivity of thermal creep requires that irradiation of the specimens should be conducted at near constant temperature which will typically be of the order of 700.degree. C. However, there are difficulties in obtaining constant temperature in reactors when, for example, the reactor operating conditions vary and the reactor is not at full power with full flow of coolant. Consequently, to achieve near constant temperature irradiation of specimens independently of reactor variations, there is a need for effecting compensation of fluctuation in temperature.